Video special effects of changing from a first video image "A" to a second video image "B" are generally known. Examples that are generally known include page rolling and page turning.
In page turning, a corner of the first image is generally shown to lift and fold over, thereby exposing a second image. The corner is then moved diagonally across the first image thereby exposing larger and larger portions of the second image. As the corner of the first image lifts and is folded-over the area of the front side near the fold becomes distorted and, a backside of the lifted corner is displayed as a reversed portion of the first image, which lifted corner then continues to fold over as it moves across the first image covering larger and larger portions of the first image as the first image is completely replaced by the second image.
In page rolling, a corner (or even a whole side) of the first image is seen to lift and roll across the screen covering the first image and exposing the second image. A reversed backside of the first image is displayed as a rolling cylinder which rolls over the first image.
Alternatively, the first image will be seen to form parallel waves across the screen with the first image following the peaks and valleys of the waves. The waves of the first image may then be swept off the screen from one side to the other as the first image is replaced by the second image.
Often the parallel waves will be seen to slope from left to right or right to left forming an angle of .theta. with the x or y axis along an effect axis when viewed from the bottom to the top of the screen. Where the peaks of the waves of the first image appear at the bottom of the screen, portions of the second image will become visible below the wave peaks of the first image.
Similarly when page turning is used, the first image, on the page being turned, is typically made to appear distorted where the corner of the first image is lifted to turn the page. The distorted area of the first image follows the folded-over corner of the first image as the page is turned to reveal the second image.
A number of known processes are available for providing page turning video effects. One known technique requires a complicated vector analysis process to track a turned edge of the first image. A vector origin that may or may not coincide with a corner of the image is first determined. A coordinate system corresponding with the turned edge of the image is then imposed on the page turning process. The results of the vector analysis is then used to access data for forming the image within non-linear portions of the turned page.
Such techniques require a double buffer for storing video information. The first buffer stores the prior image while the second buffer stores the page turning graphics generated through vector processing. A video switch is then used to switch between the second buffer providing the graphics for the first image and the buffer providing the second image.
While prior art techniques are effective in creating the complicated graphics associated with page turning and the like, the process of generating such graphics is computationally intensive. The computational intensity and complexity of such processing also limits the flexibility of such systems.
Other examples of a page turning video graphics divide the video screen into a number of different boundary areas divided by a number (e.g., three) of parabolic boundary lines and one straight boundary line. The locations of the boundary lines are determined by solving four equations. To simplify the computational complexity, a processor first identifies intersection points of the boundary lines for each step of the page turning process and then calculates a parabolic and linear position for the boundary lines. A video switch then switches from a first to a second video image, from the first video image to a blank image (backside of the first video image), or from the blank image to the second video image based upon which boundary line is crossed.
Conventional rendering techniques, such as described above, generate page turning effects by splitting the rectangular image into several portions: a) previous image; b) distorted previous image; c) distorted reverse side of previous image; and d) next image. The boundaries between the portions may be defined by circles, lines, or parabolas.
Conventional methods and apparatus create the effect of geometrical distortions by using circular or parabolic mapping processes. However, visual observations of a person actually turning a page reveal that such circular-shaped boundaries do not provide an accurate rendition of page turning. Also, since the special effect of the geometrical distorted portion is created one horizontal scan line at a time, the creation of a high quality special effect image involving geometrical distortion is inherently computationally intensive.
Conventional methods also typically process the video signals real-time. Since real-time video signals (NTSC and PAL broadcast standards) provide one scan line at a time, the conventional method must render one horizontal scan line at a time to keep up with the real-time video source. If non-horizontal rendering is used, frequently there are gaps in the rendered portions of an image (i.e., not all pixels in the rendered area are guaranteed to be rendered).
While the known processing systems perform adequately, such systems do not make efficient use of video processing resources. Conventional rendering techniques either perform complex calculations to obtain needed high quality video images or completely avoid the complex calculations at the expense of providing a lesser quality image. Because of the importance of video processing, a need exists for a means of rendering video imaging special effects that is less computationally intensive.